High power microwave system having low duty cycle

ABSTRACT

A microwave system is disclosed wherein a microwave module is capable of providing a high power pulse of short duration with long off-duty periods. Standby means which may include a separate power source are provided to cause the electron discharge device powering the module to conduct during the off-duty periods. In a preferred embodiment, switching means to disconnect the power source from the electron discharge device during the duty cycle are also provided.

PATENTEDJAI 9l873 3,710,144

sum 1 UF 2 FIG.|.

PL A TE PULSE SOURCE SOURCE OF 0.6. VOLTAGE INVENTORS:

ARTHUR L. JACKSON, 1

SHELBY A. JOLLY, JOHN B. QUIRK,

THEIR ATTORNEY United States Patent 1 1 Jackson et al. 14 1 [54] HIGH POWER MICROWAVE SYSTEM 2,577,578 12/1951 Hadfield ..328/227 x HAVING Low DUTY CYCLE 3,569,775 3 1971 l-lalsted ..315 105 2,428,008 9/1947 Brakel et al. ..3l5/l05 Inventorsi Arthur Jlcksmh Owensboro, Y 2,627,051 1 1953 Barco ..315/105 x Shelby A- Jolly, Rockport, Ind.; 3,229,211 1 1966 Pintell 328/10 X John B. Qilllk, Owensboro, Ky. 3,529,207 9/1970 Webb 315/105 X I 10 dl 9 [73] Assignee: General Electric Company 3536'952 H970 Fm Cy 315/3 [22] Filed: June 29, 1971 Primary ExaminerJohn S. Heyman Assistant Examiner-R. C. Woodbridge [2!] Appl' 7 Att0meyNathan J. Cornfeld et al.

52 us. Cl. ..307/260, 315/39, 315/105, ABSTRACT 328/101 328/227 A microwave system is disclosed wherein a microwave [51] it. Cl. "H0311 5/01 module is capable of providing a g power pulse f [58] n 8", "307/260; 313/198 199; 315/391 short duration with long off-duty periods. Standby 315/105; 328/10, 219, 223, 227, 2 7 means which may include a separate power source are provided to cause the electron discharge device 1 [56] References C'ted powering the module to conduct during the off-duty UNITED STATES PATENTS periods. In a preferred embodiment, switching mean s v to d1sconnect the power source from the electron 3,369,188 2/1968v Stover et al ..328/227 X discharge device during the duty cycle are also pro- 3,440,486 4/1969 Goldie et al. ..3l5/39 vid d 3,488,555 1/1970 Fritz ..3l5/39 2,735,012 2/1956 Werth et al ..328/l0 X 3 Claims, 3 Drawing Figures PLATE SO JIfsouncs OF 0.0. VOLTAGE Jan. 9, 1973 HIGH POWER MICROWAVE SYSTEM HAVING LOW DUTY CYCLE BACKGROUND OF THE INVENTION off-duty periods between the pulses which, for eXaml0 ple, could be as long as 24 hours.

While such long off-duty periods are not necessarily deleterious for the electron discharge device powering the module, the additional need for high power output during each pulse has created a problem. For the tube to instantaneously deliver a high power output signal during the pulse, the source of electrons, i.e., the cathode, must be capable of emitting, for example, 40-80 amperes/cm during the pulse.

To be capable of emitting at such levels, the cathode of an electron discharge device must be maintained at a high temperature. It has been found that the life of the device, when operated in this mode, is considerably shortened. While the reasons for this are not entirely known, it is presumed that the exposure of the cathode material to such high temperatures and the lack of concurrent conduction through the tube has a deleterious effect on one or more of the electrodes within the tube.

During the formation of electron discharge devices, it is known that certain materials comprising the cathode are activated by applying voltages to the electrodes to cause current to flow from the cathode to either the grid or the anode or both. It is also known that the continued application of such voltages during an aging period in the manufacture of the tube results in better subsequent performance of the tube in an actual circuit. Such aging can be at a DC voltage or may be AC such as a 1-10 KI-Iz.

It is an object of this invention to provide a microwave system comprising a microwave module capable of functioning at high power, low duty cycle periods. It is another object of this invention to provide a microwave system containing means for operating an electron discharge device in a microwave module in a standby mode during the off-duty periods without interfering with the duty cycle of the system. It is yet another object of the invention to provide means for obtaining substantially continuous current flow from the cathode of the electron discharge device. These and other objects of the invention will be apparent from the drawing and following description.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a wiring diagram of a preferred embodiment of the invention showing the module in cross-section.

FIG. 2 is an'altemate embodiment of the invention. FIG. 3 is another alternate embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, a microwave module is 10 is heated by a heater 12 having leads l4 and 16 to a convenient source of heater power such as battery 18. The output electrode 20, which in the illustrated figure, is the anode of device 4, is coupled through a resistor 24 to a pulse source indicated in the block diagram at 30.

In the illustrated embodiment of FIG. 1 a third, grid, electrode 40 is connected through a resistor 42 to anode resistor 24 at 44. A voltage divider 50 comprising seriesconnected resistors 51 and 52 is also connected to point 44 with the opposite end of the divider grounded. Grid 40 is also connected through a resistor 58 to a switch 60 which, in the illustrated embodiment, is a PNP transistor. Resistor 58 is connected to collector 62 of transistor 60. The base 64 of transistor 60 is connected to a mid-point 53 on voltage divider 50 between resistors 51 and 52. The emitter 66 of transistor 60 is connected to a source 70 of positive voltage conveniently, for example, about 12 volts DC.

The system then functions as follows: During the time the source of pulse power 30 is supplied to anode 20 of electron discharge device 4, the voltages across resistors 51 and 52 comprising the voltage divider 50 between ground and the plate provide a bias at point 53 such that the base-emitter bias of transistor 60 turns transistor 60 off. Upon cessation of the pulse the voltage divider 50 becomes more negative biasing the baseemitter into an on position allowing the 12 volt positive voltage of source 70 to flow from emitter 66 to collector 62 and through resistor 58 to grid 40 enabling electron discharge device 4 to conduct current from cathode 10 to grid 40. When the pulse again turns on, transistor 60 is again turned off causing the current flow from cathode 10 to grid 40 to again cease.

In this manner, regardless of the length of the offduty cycle of the high power pulse, cathode 10 remains in a conductive mode due to the DC voltage intermittently applied through switch 60 to grid 40. While the exact mechanism by which the invention functions is not fully understood, the application of current through the cathode apparently has the effect of preventing the cathode materials from being deleteriously affected by the high-temperature maintained on the cathode by heater l2. Utilizing voltage divider 50 and switch 60, the current so applied does not have a harmful effect upon the actual duty cycle or pulse period of the device 7 and thus the normal function of the device is not interfered with.

Referring now to FIG. 2, another embodiment of the invention is illustrated. In this embodiment, the source of positive voltage to be applied to grid 40 is derived from the plate pulse source through a capacitor 80. Grid 40 is connected to ground through a resistor 82. The values of capacitor and resistor 82 are selected to provide an R-C time constant less than the delay time between application of the pulse and the commencement of oscillation. By preselecting the proper time constant the activating current supplied to grid 40 will have decayed sufficiently by the time the oscillator begins to oscillate to not interfere with the signal. While in this embodiment the duty period is enlarged, that is the period in which current is flowing from the cathode, long periods between pulses must be avoided. Thus while the circuitry is much simpler than that illustrated in FIG. 1, the application of the system in FIG. 2 is more limited.

In yet another embodiment illustrated in FIG. 3, an independent source of positive voltage is connected to grid v40 through an impedance 90 which may comprise the various combinations of resistance, inductance and capacitance well known tothose skilled in the art. In this embodiment the positive voltage is constantly maintained on grid 40 and thus, current flows from cathode continuously whether the module is in a standby or duty mode. This embodiment is preferred over that shown'in FIG. 2 when long standby periods are to be encountered while the embodiment illustrated in FIG. 2 is preferred over that shown in FIG. 3 when the standby current flow would interfere with the signal during the duty cycle.

'Thus our invention provides means for operating a microwave module at high power with long standby periods or low duty cycles without the deleterious consequences previously encountered in the art. While several embodiments have been illustrated, the preferred embodiment is that shown in FIG. 1 whereby the system will function satisfactorily substantially independent of the length of the off-duty or standby cycle yet the standby current will be shut off during the duty cycle.

What is claimed is:

1. A microwave system comprising: a microwave module; an electron discharge device within said module including a first electrode capable of emitting electrons and at least one other electrode; means for applying a pulse to said electron discharge device; and means for applying a positive voltage to a grid electrode in said device between said pulses through switch means which disconnect the positive voltage from the grid during the pulse to cause electrons to flowfrom said first electrode.

2. A microwave system capable of high power output at low duty cycles comprising: a microwave module; an electron discharge device within said module comprising an electron tube having a cathode, an anode, and at least one grid, means for applying a pulse connected to said anode, switching means comprising a solid state switch, and a source of positive voltage connected through said switch to apply said positive voltage to said grid between pulses to cause said cathode to emit electrons, said switch means being coupled to said pulse means to turn off said switch means during the pulse.

3. The system of claim 2 wherein said control element is coupled to said pulse means by a voltage divider between said pulse means and ground whereby said control element acts in response to a voltage change in said divider. 

1. A microwave system comprising: a microwave module; an electron discharge device within said module including a first electrode capable of emitting electrons and at least one other electrode; means for applying a pulse to said electron discharge device; and means for applying a positive voltage to a grid electrode in said device between said pulses through switch means which disconnect the positive voltage from the grid during the pulse to cause electrons to flow from said first electrode.
 2. A microwave system capable of high power output at low duty cycles comprising: a microwave module; an electron discharge device within said module comprising an electron tube having a cathode, an anode, and at least one grid, means for applying a pulse connected to said anode, switching means comprising a solid state switch, and a source of positive voltage connected through said switch to apply said positive voltage to said grid between pulses to cause said cathode to emit electrons, said switch means being coupled to said pulse means to turn off said switch means during the pulse.
 3. The system of claim 2 wherein said control element is coupled to said pulse means by a voltage divider between said pulse means and ground whereby said control element acts in response to a voltage change in said divider. 